The present invention relates to cement mixing equipment and, in particular, to a conveyer auger for blending mixture components over the length of the augerway, prior to the concrete exiting an outlet port.
Varieties of cement mixers have been developed over the years to accommodate the needs of various users. Such mixers range in size from small trailerable, pot-like units having a motor driven revolving drum, which are hand fed with mixture components, to multi-story assemblies which are fully automatic.
One mixer type within this broad range and relative to which the present invention is particularly directed are mixers which are used by pre-casters for manufacturing stairs, septic tanks and the like. Such mixers are sized to mix approximately 20 yards before re-filling of the aggregate mixture bins and may only mix on the order of 100 yards of concrete over the course of a typical day. The concrete is particularly prepared on a semi-continuous or batch basis as forms are stripped and readied to receive the concrete.
To meet the needs of this class of users, Applicants have developed a mixer which is marketed as a model WDZ-200 Such mixers generally provide a multi-compartmented housing whereat sufficient quantities of gravel, sand and cement are contained and automatically fed under operator control in relatively precise volumes. A bulk cement storage silo can also be attached to the mixer.
The mixture components are otherwise metered via a unitary drive train and deposited through controlled apertures at the infeed end of a related blending auger which mounts to the forward end of the housing. More of the details of this mixer can be found upon directing attention to Applicant's related promotional literature or U.S. Pat. No. 4,922,463, filed Aug. 22, 1988 and entitled Portable Volumetric Concret Mixer/Silo.
From such materials, it is to be noted that Applicant has previously used a fixed length, spiral fluted auger assembly to effect blending of the mixture components over the length of travel of the auger. Blending cycle time has been controlled relative to a constant, fixed RPM drive speed by controlling the relative angle of the auger assembly to the mixer via an associated boom control. Constant uniform blending and conveyance of the concrete is, in turn, effected via rotation of the solid bodied auger flutes.
Depending upon the intended use of the concrete and the nature of the mixture components, Applicant has however discovered that sufficient agitation and blending may not always occur over the length of the relatively short augerway. Although a longer augerway or a variable drive might be substituted. A longer augerway and/or a variable speed auger drive, also significantly add to the cost of the mixer.
A need therefore exists for a new type of auger assembly which provides a stepped or segmented agitation of the mixture over the length of the auger, without resort to a variable motor drive and which further permits a suitable range of blending cycle times to effect optimal mixing.
Relative to various concrete mixing assemblies of which Applicants are familiar and which include fluted conveyer augers, assemblies are disclosed in U.S. Pat. Nos. 3,153,494; 4,298,288; and 4,624,575. Within each of these patents, helical, full-webbed augers are disclosed which are principally used to convey selected materials over the length of various mixer assemblies.
Applicants are also aware of British Patent No. 2,090,761 which discloses a two-stage, high speed, shear mixer. A first stage particularly includes a ribbon portion a plurality of paddle portions and a ribbon portion which serially convey a cement slurry to a second stage which includes a plurality of paddles. The stages otherwise are contained within a fully enclosed housing and are intended to operate at high rates of revolution, with relatively short path lengths, to mix grouts, plasters, gypsum and other nonaggregate containing mixtures. Material transfer occurs by way of a shear action that is created between the ends of the augers and the housing walls. In contrast, the augerway of the present invention is intended to mix and transfer concrete or other materials including relatively large concentrations of coarse aggregates by way of the auger flights.